TEMPERATURE DEPENDENT (83-483 K) RAMAN SPECTROSCOPY ANALYSIS OF CVD GROWN WS2 MONOLAYERS

For novel materials to be used in practical applications, their temperature dependent behavior and limitations need to be understood thoroughly. For example, the mobility of charge carriers, one of the important performance parameters in transistors, strongly depend on the change in the ambient temperature. Hence, characterization of potential optoelectronic materials at extreme temperatures is critical for future applications. In this study, we report on the changes of Raman scattering spectra as the temperature is changed from 83 K to 483 K for the 2D transition metal dichalcogenide materials, namely WS2 monolayers formed by chemical vapor deposition technique (CVD). Our results show that both E′ (E12g) and A1(A1g) modes red shift linearly as the temperature increases. The first order thermal coefficients have been calculated with the Gruneisen model, which suggests that in-plane mode is affected more by the increased temperature than that of out of plane mode. This difference is attributed to the defects in the sample as the flakes are grown by the CVD method. We also investigated the temperature dependence of the second order, 2LA(M) (at 345.7 cm-1) which is one of the most intense peaks in the spectra.